The invention relates to an intraocular multifocal lens, and methods of manufacture and utilization thereof. The need for and advantages of the invention are best understood by reviewing the background in the normal operation of the accommodative mechanism of the eye.
Using the most accepted explanation of accommodation, that of Helmholtz, it is known that as an object approaches an emmetropic or artificially emmetropic eye the rays from the object become more and more divergent. If the eye remains unchanged, the refracted rays strike the retina before coming to a focus. Thus, the object appears blurred (blurred, but not distorted). In the normal visual system this blur is the mechanism that triggers the brain to cause the ciliary muscles to contract which allows the crystalline lens to increase its plus power in order to focus the diverging rays on the retina to produce a clear image. Thus the eye accommodates itself to the nearer object so as to obtain a clear image. Objects closer or further are blurred, but not distorted, and are ignored unless they become the new object of interest.
In eyes which have lost all (as in cataract extraction, aphakia) or part of their accommodative mechanism as with presbyopia (due to increased age and usually beginning between ages 40-45) this focusing at near is either lost or reduced, the severity depending upon the condition of the eye and age of the individual. Normally, a bifocal spectacle or bifocal contact lens is prescribed so that the patient has clear vision at the far point (i.e. 20 feet and beyond) and at reading distance. By definition a bifocal has two foci, one for far vision and one for near. If the difference between these powers is significant there is an intermediate range of blurred vision between near and far.
In order for the wearer to use the different powers of the average bifocal his or her eye must look through one part of the lens for distance vision and through the other part of the lens for near vision. This requires that the patient holds his or her head up and his or her eyes down in an abnormal position in order to see at near. Since there is a line of demarcation between these two powers he or she sees a split image as his or her eye passes across this junction, and notices objects change position as the powers change suddenly (commonly termed xe2x80x9cBifocal Jumpxe2x80x9d).
Some have attempted to eliminate or at least reduce this problem by xe2x80x9csmearingxe2x80x9d the junction line between the two powers, but have really only induced a new problem, distortion. Very few people can tolerate distortion of any amount as this is an abnormal condition to the human eye and brain. As stated earlier, blur is normal and can be tolerated at least until accommodation produces a clear image.
There is a differentiation among spectacle lenses, contact lenses and intraocular lenses in the details of vision mechanism.
(1) Spectacle lenses require significant head movement so that the eyes can see through the distance, intermediate (if available) and near portions of the lens.
(2) Contact lenses must be able to move. If a contact lens does not move it will become intolerable to the eye due to dryness, deposits, edema, infection, etc.
(3) An intraocular lens, implanted in the eye, normally does not move. Thus the design of the lens regarding the distance, intermediate and near lens areas must be definitely different from the spectacle and contact lens.
What is needed to properly correct aphakia is an intraocular lens which has the following characteristics:
(a) When implanted in the patient""s eye he or she need only to look normally at objects he or she wishes to see at any distance and in any position.
(b) No definite line of demarcation between near and far so that no split image, distortion, glare, etc. is seen and the patient has clear vision at all distancesxe2x80x94far, near and intermediate.
(c) The transition between far and near powers must be smooth, gradual, and without distortion. These powers must be available to the patient so that he or she can use them to see at the intermediate distances.
It can readily be seen that with a lens as described above the patient has available all of the powers he or she needs to see clearly without distortion at any distance. His or her brain need only select the power that makes any object clear. The same triggering mechanism, blur, that is used with normal accommodation is used with this lens to cause the eye and brain to select the proper power. As with normal accommodation as stated earlier the brain ignores other blurred images until they become the object of interest.
In order to satisfy the above characteristics it is necessary to produce a lens that has all of the powers the patient needs to see clearly at any distance and make them available, without distortion, in a lens which cannot translate. Thus all of the powers must be available simultaneously in a very small multifocal zone size.
According to the present invention an intraocular multifocal lens is provided with no definite line between near and far or intermediate powers, no distortion, and no need for the lens to translate, e.g. as the patient has all of the powers in a circular conformation on either the front or back of the lens or both.
Another parameter of the lens of the invention is that the very center of the lens should be the distance or far correction surrounded by the intermediate powers and finally the near or reading powers. While the lens could be made in reverse, with the near in the center surrounded by the intermediate powers and then by the distance power, this relationship does not normally perform as well and is not recommended.
The process for producing a multifocal intraocular lens differs from that used to produce multifocal contact lenses, or other lenses, in several ways:
(1) The multifocal zone size is smaller in the intraocular lens since the lens does not move, is closer to the retina than a contact lens and is very close to the iris and pupil. The zone size may be determined by evaluating the length of the eye by using an xe2x80x9cAxe2x80x9d scan along with the necessary power of the correcting lens and the pupil size. A longer eye might need a larger zone size as would a lens which does not center well. While a smaller pupil size might require a smaller zone size as would a shorter eye. While the multifocal zone size can be varied as discussed above it has been found by extensive research and trial and error that a uniform zone size of about 2.5-3.5 (e.g. about 3) mm in diameter for essentially all adults is appropriate.
(2) Working with intraocular lenses is considerably different than with spectacle or contact lenses. Since the eye is aphakic and the lens will be implanted in aqueous, intraocular lenses average about 17-24 diopters in aqueous and about 52-73.5 in air while contact lenses and spectacle lenses average about 1-4 diopters in air.
(3) Also, the diameter of an intraocular lens is usually about 5-6.5 mm, e.g. about 6 mm, but can vary considerably, while contact lenses are usually about 9-14 mm and spectacle lenses are considerably larger than the other two and vary greatly in size and shape.
According to one aspect of the present invention an intraocular multifocal lens is provided. The intraocular multifocal lens according to the invention has no definite line between near, far, or intermediate power lens areas, and substantially no distortion.
In the preferred construction of the multifocal lens of the invention, the lens has substantially concentric and substantially circular near, intermediate, and far power lens areas. Preferably the far power lens area is centrally located in the lens, and at least one intermediate power lens portion is between the near and far power lens areas. Preferably the multifocal zone is about 2.5-3.5 mm (e.g. about 3 mm) in diameter. While the invention in its simplest form may comprise only three different curvature areas, it is to be understood that in the preferred embodiment there are many, many (perhaps several hundred or more) slightly different powers in each of the near, intermediate, and far areas, and the terminology is to be interpreted with this in mind.
Typically the lens has a front surface adapted to be remote from a user""s retina, and a rear surface adapted to be closer to a user""s retina; and the near, intermediate and far power lens areas are formed in at least one of the front and rear surfaces. The near, intermediate, and far power lens areas may be formed only in the front surface, only in the rear surface, or both the front and rear surfaces. Typically the lens has a diameter of about 5-6.5 mm, e.g. about 6 mm, and a diopter of between about 52-73.5 in air. No aspheric curve which causes distortion, but rather a multiplicity of spherical powers, is provided for the lens according to the invention.
According to another aspect of the present invention there is provided (a) producing an intraocular multifocal lens having no definite line between near, far, or intermediate power lens areas, and substantially no distortion. And (b) placing the intraocular lens from (a) in a human""s or animal""s eye.
In the preferred method of the invention, (a) is practiced by mechanically acting on a curved surface of a single vision lens which has the power of the human""s (or animal""s) near eye prescription to provide lens areas thereof that have intermediate and far power for the patient. Also, (a) may be further practiced by forming the intermediate and far power lens areas so that they are substantially circular in configuration and substantially concentric. Still further, (a) may be practiced so that the intermediate power lens area is concentric with and surrounds a far power lens area that is substantially centrally located in the lens, and the near power lens area surrounds the intermediate power lens area. For example (a) is further practiced using a spinner shaft and a spinning dish having fabric tightly stretched thereover, and by (a1) releasably fixing the lens to the spinner shaft preferably with the curved surface convex and facing away from the spinner (although the back surface could be flat, concave or convex), (a2) disposing the spinner shaft at an angle to the axis of rotation of the fabric covered dish; (a3) rotating at least one of the spinner shaft and dish, and (a4) operatively bringing the curved surface of the lens into contact with the rotating fabric (by moving at least one of the lens and fabric).
Alternatively, (a) may be practiced by producing a mold having desired lens area configurations, and then filling the mold with fluid lens material, causing the fluid lens material to harden to form the lens, and then removing the lens from the mold, or by using a laser lathe.
According to another aspect of the present invention there is provided a method of producing an intraocular multifocal lens using a single vision lens having a curved surface, using a spinner shaft, and a dish having fabric tightly stretched thereof, comprising: (a1) releasably fixing the lens to the spinner shaft with the curved surface convex and facing away from the spinner, (a2) disposing the spinner shaft at an angle to the axis of rotation of the fabric covered dish; (a3) rotating at least one of the spinner shaft and dish, and (a4) operatively bringing the curved surface of the lens into contact with the rotating fabric, to form near, intermediate, and far power lens areas that are substantially circular and substantially concentric with each other. In the practice of this aspect of the invention, preferably the single vision lens has a near power prescription for a particular human or animal eye, and (a1)-(a4) are practiced to provide a central far power lens area surrounded by an intermediate power lens area, in turn surrounded by a near power lens area. Also preferably (a1)-(a4) are practiced so that the multifocal zone formed by the near, intermediate, and far power lens areas has a diameter that is about 2.5-3.5 mm. The invention also preferably comprises an intraocular multifocal lens constructed by the method described above.
It is the primary object of the present invention to provide a highly effective intraocular multifocal lens which does not have the drawbacks associated with conventional bifocals or multifocals. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.